In engines such as four-cycle four-cylinder engine, a secondary inertia force is produced at the center of gravity of the piston-connecting rod system.
Taking this into account, some engines are equipped with a balancing device where the balancer shaft is rotated twice as fast as the revolution speed of the engine to compensate the secondary inertia force.
Also, the balancing device is sometime disposed directly under a crank case taking into consideration the assembly or the lubrication system.
Further, it is known that, for downsizing the balancing device, the balancer weight can be formed of two parts, the first part being formed of a first balancer weight disposed between two balancer shaft bearings; and the second part being formed of a second balancer weight cantilevered or projecting at a position opposing the first balancer weight, a balancer shaft bearing being positioned between the first and the second balancer weights.